A known diode includes on a cathode side an (n−) doped drift layer, and on an anode side opposite to the cathode side a p doped anode layer. On top of the p doped anode layer, a metal layer which functions as an anode electrode is arranged. On the cathode side, a higher (n+) doped cathode layer is arranged. A metal layer in the form of a cathode electrode is arranged on top of the (n+) doped cathode layer.
Such devices are created by making one ion diffusion for the anode contact layer and another ion diffusion for the anode buffer layer. By this method, first ions for the anode buffer layer are implanted and deeply diffused into a wafer into a depth of around 20 μm, and afterwards, second ions are implanted and diffused into a depth of around 5 μm.
FIG. 11 shows the doping profiles of known p doped anode layers (split A and B), which include a highly doped and shallow anode contact layer and a deeper diffused, but lower doped anode buffer layer. The maximum doping concentration of the anode contact layer is around 5*1018 cm−3.
The anode buffer layer can be optimized either for leakage current, for which a high doping concentration is needed in a low depth of 5 μm, e.g., a doping concentration higher than 1*1016 cm−3 in 5 μm depth is used for such devices (Split A). Such a high doping concentration in 5 μm has the consequence that the doping concentration in a larger depth of 15 μm is also as high as 7.2*1014 cm−3. This is the consequence from using a single diffusion for the anode buffer layer. However, the high doping concentration in 15 μm has disadvantages for the soft turn off of the device.
Therefore, other devices are made, which are optimized for soft turn off of the device, which requires a deep, but low doped anode buffer layer, which is achieved by having a low doping concentration of 1.5*1014 cm−3 in 15 μm depth (Split B). However, this can only be achieved by also lowering the doping concentration in 5 μm to 4*1015 cm−3, which value is again unfavourable for the leakage current.
With such known devices, it is not possible to influence the curvature of the doping concentration profile, and thus, it is not possible to optimize leakage current and softness simultaneously in one device.